Chip-interleaved, block-spread multi-user communication

ABSTRACT

Techniques are described for maintaining the orthogonality of user waveforms in multi-user wireless communication systems, such as systems using the code division multiple access (CDMA) modulation scheme in the presence of frequency-selective fading channels. Unlike conventional systems in which spreading is performed on individual information-bearing symbols, the “chip-interleaved block-spreading” (CIBS) techniques described herein spread blocks of symbols. A transmitter includes a block-spreading unit to form a set of chips for each symbol of a block of information-bearing symbols and to produce a stream of chips in which the chips from different sets are interleaved. A pulse shaping unit within the transmitter generates a transmission signal from the stream of interleaved chips and transmits the signal through a communication channel. A receiver includes a block separator to de-interleave the chips, followed by a match filter to separate signals from different users, and followed by any single-user equalizer.

This application claims priority from U.S. Provisional Application Ser.No. 60/274,365, filed Mar. 8, 2001, the contents being incorporatedherein by reference.

This invention was made with government support under ECS-9979443awarded by the National Science Foundation. The government has certainrights in the invention.

TECHNICAL FIELD

The invention relates to communication systems and, more particularly,transmitters and receivers for use in multi-user communication systems.

BACKGROUND

In multi-user wireless communication systems, such as mobile phonenetworks, wireless local area networks and satellite communications,multiple transmitters and receivers may communicate simultaneouslythrough a common wireless communication medium. One communication formatwidely used by multi-user systems is Code Division Multiple Access(CDMA), in which the transmitters generate orthogonal waveforms that canbe separated by the receivers. More specifically, each transmitterapplies one code chosen from a set of orthogonal “spreading codes” to anoutbound serial stream of “symbols.” Each symbol represents a discreteinformation bearing value selected from a finite set (“alphabet”). Forexample, simple alphabets used by transmitters may be {+1,−1} or{−3,−1,+1,+3}. The application of the orthogonal spreading codes to thesymbols produces a set of “chips” for each symbol to be transmitted. Theresulting chips are transmitted according to some modulation scheme,such as quadrature phase shift keying (QPSK) modulation. In order toseparate signals from multiple users, the receivers isolate the signalof the desired user by matching the signal to the correspondingorthogonal spreading code.

When the transmission rate increases, the communication medium canbecome “frequency selective” in that certain frequencies exhibitsignificant fading, i.e., significant loss of signal. This propertyoften causes inter-chip interference (ICI) in which the transmittedchips for a particular symbol interfere with each other, destroying theorthogonality of the waveforms at the receiver. By rendering thetransmitted waveforms non-orthogonal, ICI can lead to multiple userinterference (MUI), in which the receivers are unable to correctlyseparate the waveforms, eventually leading to data loss and/or bandwidthand power inefficiencies.

Various techniques have been developed that attempt to suppress theeffects of MUI. For example, various “multi-user detectors” have beendeveloped for separating non-orthogonal user waveforms. These detectors,however, typically use techniques that require knowledge of thecharacteristics of the current communication medium and that are oftencomplex and expensive to implement in typical mobile communicationdevices. In addition, alternatives to CDMA have been proposed includingmulticarrier (MC) spread spectrum based multiple access, e.g.,(generalized) MC-CDMA and Orthogonal Frequency Division Multiple Access(OFDMA), where complex exponentials are used as information-bearingcarriers to maintain orthogonality in the presence of frequencyselective channels. Multicarrier schemes are power inefficient becausetheir transmissions have non-constant magnitude in general, which causespower amplifiers to operate inefficiently. These alternatives can alsobe very complex and expensive to implement and do not necessarilycompensate for channels that introduce significant fading.

SUMMARY

In general, the described invention provides an efficient technique formaintaining the orthogonality of waveforms in multi-user wirelesscommunication systems, such as systems using the code division multipleaccess (CDMA) communication formats. Unlike conventional systems inwhich spreading is performed on a per symbol basis, the“block-spreading” techniques described herein operate on blocks ofsymbols. Furthermore, the resulting chips are interleaved such that thechips generated from any particular symbol are temporally spaced andseparated by “guard” chips. In this manner, the symbol-bearing chips andguard chips are transmitted and received in an alternating format.

In one embodiment, the invention is directed to a system in which atransmitter includes a block-spreading unit to form a set of chips foreach symbol of a block of information-bearing symbols and to produce astream of chips in which the chips from different sets are interleaved.A pulse shaping unit within the transmitter generates a transmissionsignal from the stream of interleaved chips and transmits the signalthrough a communication channel. A receiver includes a block separatorto de-interleave the chips prior to user separation.

In another embodiment, the invention is directed to a transmittingdevice having a symbol-spreading unit to apply a user-specificorthogonal spreading code to each symbol within a block of symbols,thereby forming chips. A buffer stores the resulting chips in an arrayand pads the chips with “guard” chips. In one configuration the arraycomprises M columns and K+L rows, where K is the number of symbols perblock, L represents the number of guard chips and is a function of thecommunication channel length, and M represents a maximum number ofusers. The buffer stores the chips such that each row in the arraycontains chips generated from the same symbol. A chip-interleaving unitwithin the transmitting device reads the chips column-wise from thebuffer and outputs a stream of chips in which the chips from differentsets are interleaved.

In another embodiment, the invention is directed to a method in which aset of orthogonal spreading codes is applied to a block ofinformation-bearing symbols to form a set of chips for each symbol.Chips from the chip sets are selected in an order that produces a streamin which the chips from different sets are interleaved. A transmissionsignal is generated from the stream of interleaved chips.

In yet another embodiment, the invention is directed to acomputer-readable medium having instructions thereon. The instructionscause a programmable processor to apply a set of orthogonal spreadingcodes to a block of information-bearing symbols to form a set of chipsfor each symbol. The instructions cause the programmable processor toselect chips from the chip sets to produce a stream of chips in whichthe chips from different sets are interleaved, and generate atransmission signal from the stream of interleaved chips.

The chip-interleaved block-spread communication techniques describedherein offer many advantages. By interleaving the chips generated fromblocks of symbols, the transmitter and receiver are resistant tomulti-user interference (MUI), regardless of the underlying frequencyselective nature of the communication channel and without using adaptivepower control to dynamically adjust the usage of power by transmitter.Because the chips generated from a common symbol are temporally spacedand separated by guard chips, interference experienced duringpropagation through the channel will cause inter-symbol interference,but inter-chip interference is avoided. Therefore, the spreading codesfor the various users may remain orthogonal regardless of channeleffects.

Other advantages of block spreading include improved bandwidthefficiency, which implies that information can be transmitted at higherrates and that the maximum allowable number of simultaneous usersincreases. Furthermore, because the waveforms remain orthogonal, thetechniques allow receivers to use single-user detectors, which are lesscomplex than multi-user detectors. In other words, the techniques allowreceivers to be configured with low complexity detectors that achieveperformance equivalent to a set of M single user detectors. Thetechniques can be easily used with existing code-generation schemes thatgenerate orthogonal spreading codes.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a wireless system in whichmultiple transmitters communicate with multiple receivers through achannel.

FIG. 2 is a block diagram illustrating in further detail the multi-usercommunication system of FIG. 1.

FIG. 3 is a block diagram illustrating an example embodiment of ablock-spreading unit within a transmitter.

FIG. 4 illustrates an example mode of operation of the block-spreadingunit.

FIG. 5 illustrates an example data stream generated by asymbol-spreading unit within the transmitter.

FIG. 6 illustrates an example data stream generated by achip-interleaving unit within the transmitter.

FIG. 7 illustrates an example arrangement of the chips stored within abuffer in array format.

FIG. 8 is a flowchart illustrating an example mode of operation ofcommunication system in which a transmitter and a receiver communicateusing chip-interleaved block-spread communications.

FIGS. 9, 10 and 11 are graphs illustrating modeled performance estimatesof the chip-interleaved block-spreading techniques described herein.

DETAILED DESCRIPTION

FIG. 1 is a block diagram illustrating a multi-user wirelesscommunication system 2 in which multiple transmitters 4 communicate withreceivers 6 through wireless channel 8. In general, the inventionprovides an efficient technique for maintaining the orthogonality ofwaveforms produced by transmitters 4, thereby suppressing any effects ofmulti-user interference (MUI) 9 that could otherwise be introducedduring transmission through communication channel 8.

Transmitters 4 transmit data using a multi-user spreading schemereferred to herein as “chip-interleaved block-spreading” (CIBS). Thisscheme can work with existing spreading code generating schemes and,therefore, is backward compatible with a number of conventionalmulti-user transmission formats including Code Division Multiple Access(CDMA) and Orthogonal Frequency Division Multiplexing (OFDM). The formeris an example of single-carrier multiple access scheme, while the latteris a multi-carrier scheme. OFDM has been adopted by many standardsincluding digital audio and video broadcasting (DAB, DVB) in Europe andhigh-speed digital subscriber lines (DSL) in the United States. OFDM hasalso been proposed for local area mobile wireless broadband standardsincluding IEEE802.11a, MMAC and HIPERLAN/2.

The techniques described herein apply to uplink and downlinktransmissions, i.e., transmissions from a base station to a mobiledevice and vice versa. Transmitters 4 and receivers 6 may be any deviceconfigured to communicate using a multi-user wireless transmissionincluding a cellular distribution station, a hub for a wireless localarea network, a cellular phone, a laptop or handheld computing device, apersonal digital assistant (PDA), a Bluetooth™ enabled device and thelike.

FIG. 2 is a block diagram illustrating in further detail the multi-usercommunication system 2 of FIG. 1. Generally, multiple transmitters 4corresponding to different users use orthogonal spreading codes togenerate transmission waveforms 20 in which the codes remain orthogonalduring communication to receiver 6 through channel 8. Serial to parallel(S/P) converter 12A of transmitter 4 parses outbound data 23 from aserial data stream of symbols into blocks of K symbols 29, each symbolrepresenting a discrete information bearing value selected from a finitealphabet.

As described in detail below, CIBS unit 14 applies an a user-specificorthogonal spreading code of length M to each of the symbols to producea set of “chips” for each symbol, thereby spreading the data for eachsymbol. CIBS unit 14 may, for example, apply a user-specific spreadingcode of {−1,−1,+1,+1}, in which M equals 4. Next, CIBS unit 14interleaves the chips to produce data stream 25. Parallel to serial(P/S) converter 16A converts the interleaved chip data into a serial bitstream, from which pulse shaping unit 17 forms transmission waveform 20,which is a continuous time signal for carrying the chip-interleaved,block-spread data through channel 8.

Generally, CIBS unit 14 can be viewed as producing P interleaved chipsfrom blocks of K symbols, where P can be determined as follows:P=M*(K+L).L represents a number of spacing chips, referred to herein as “guard”chips, and is determined by the effective length of channel 8 indiscrete time, such as 5, 10 or 15 chips long. M represents the lengthof the user-specific code, i.e., the maximum number of users that can besupported simultaneously.

Receiver 6 receives incoming data stream 21, which typically is afunction of transmission waveform 20 and noise introduced by channel 8.Block separator 18 samples data stream 21 and buffers the discrete databy storing the interleaved chips in array form. Block separator 18selectively outputs blocks of chips that are associated with a commonsymbol, thereby de-interleaving the chips.

Single user detector 22 receives the de-interleaved chips from blockseparator 18 and applies a conventional matched filter to separatesusers based on orthogonality and is followed by a single-user decodingscheme to remove channel effects and output the estimated symbols.Parallel to serial converter 16B converts the stream of symbols producedby single user detector 22 into serial data stream 24. In this manner,the techniques allow transceivers to be configured with low complexitydetectors that achieve performance equivalent to a set of M single userdetectors.

FIG. 3 is a block diagram illustrating an example embodiment of CIBSunit 14 of transmitter 4. In this embodiment, CIBS unit 14 comprises asymbol-spreading unit 26 that applies a user-specific orthogonalspreading code of length M to an incoming stream of symbols 29. As such,chip buffer 27 and chip-interleaving unit 28 may be used with anyconventional symbol-spreading scheme that uses orthogonal spreadingcodes. Symbol-spreading unit 26 applies a user-specific, spreading codeof length M to produce a set of “chips” for each symbol, therebyorthogonally spreading each symbol, where M represents the maximumallowable number of simultaneously communicating users.

Chip buffer 27 receives and stores the chips in array fashion, whereeach row of the array stores M chips generated from the same symbol.Chip buffer 27 may be a dedicated hardware buffer, random access memory,or any suitable device for storing the chips. After buffering the K rowsof M chips, chip buffer 27 pads the information with L rows of “guard”chips (G), where L indicates the effective length of the channel 8 indiscrete time, such as 5, 10 or 15 chips long. The guard chips introducea guard time of length L that can be made arbitrarily negligible as theblock size (K) is increased. In one configuration, the guard chips arenull (zero) values. In another configuration, the values are drawn fromthe same modulation constellation as the current symbol, allowing forconstant modulus for the output amplifier of transmitter 4, therebyincreasing power efficiencies. Thus, in one embodiment, chip buffer 27stores an array having dimensions of [M, K+L], where M represents themaximum allowable number of simultaneously communicating users, Krepresents the number of symbols in a block and L represents a number ofguard chips. Chip-interleaving unit 28 reads and transmits the chipsfrom chip buffer 27 in column-wise fashion, thereby interleaving thechips to produce output stream 25.

FIG. 4 illustrates an example mode of operation of CIBS unit 14 whilegenerating a chip-interleaved block-spread waveform. In this example,input data stream 29 comprises two symbols to be transmitted: {A,B}.Symbol-spreading unit 26 sequentially applies a user-specific orthogonalspreading code 33 of length 4 (M equals 4) to the symbols, to producechips 21. In this example, symbol-spreading unit 26 applies a spreadingcode of {−1,−1,+1,+1} to the first symbol {A} of input data stream 29 toproduce chips {−A, −A, A, A}. Next, symbol-spreading unit 26 appliesspreading code 33 to the second symbol {B} of input data stream 29 toproduce chips {−B, −B, B, B}.

Chip buffer 27 receives and stores the generated chips 29 in matrixform. The first two rows of chip buffer 27 store the set of chipsgenerated from symbols A and B, respectively. After storing the chips,chip buffer 27 pads the information with a row of guard chips 38.Chip-interleaving unit 28 extracts data from chip buffer 27 incolumn-wise fashion, thereby interleaving the coded symbol informationto produce output data stream 25. Thus, in this example, the maximumnumber of simultaneous users (M) equals 4, the blocks of symbols thatare spread and interleaved (K) equals 2, and the channel length (L)equals 1.

It can be seen from data stream 25 that the chips for the symbols 29 areinterleaved, in that data stream 25 repeats a pattern of chips thatincludes a chip generated from symbol A, a chip generated from symbol B,and a guard chip. Within a communication cell, every user has auser-specific spreading code that is orthogonal to the spreading codesof the other users. The chip-interleaved block-spreading process can beviewed as using the user-specific spreading code 33 to create “child”orthogonal codes for each symbol in the block. For example, examinationof data stream 25 reveals that the child spreading code for the firstsymbol A can be viewed as {−1,0,0,−1,0,0,+1,0,0,+1,0,0}. Similarly, thechild spreading code for symbol B is {0,−1,0,0,−1,0,0,+1,0,0,+1,0}.

By interleaving the chips corresponding to different symbols within ablock of symbols, transmitter 4 and receiver 6 are resistant tomulti-user interference (MUI), regardless of the underlying frequencyselective nature of channel 8 and without using adaptive power controlto dynamically adjust the usage of power by transmitter 4. Interferenceexperience during propagation through the channel may cause inter-symbolinterference, but interchip interference is avoided because the chipsfor a given symbol are spaced in time and separated by guard chips.Therefore, the spreading codes for the various users remain orthogonalregardless of channel effects.

FIG. 5 illustrates in more detail data stream 21 generated bysymbol-spreading unit 26. Data stream 21 includes a sequence of chips,designated as C_((k,m)), where k identifies a particular symbol withinblock of symbols and ranges from 0 to K−1, and m identified a particularchip for the user-specific spreading code and ranges from 0 to M−1. Asillustrated in FIG. 5, symbol-spreading unit 26 outputs M chips for eachof the K symbols within a block of symbols.

FIG. 6 illustrates in more detail data stream 25 generated bychip-interleaving unit 28. Data stream 25 includes a sequence of chips,again designated as C_((k,m)). Chip-interleaving unit 28 produces datastream 25 such that the chips generated from a common symbol aretemporally distributed and separated by guard chips 42. For example, afirst set of generated chips 44A includes the first chip D_((k,0))generated from each of the K symbols, followed by L guard chips 42A. Thesecond set of generated chips 44B includes the second chip D_((k,1))generated from each of the K symbols, again followed by L guard chips42B. This pattern repeats until chip-interleaving unit 28 has extractedall M*(K+L) chips from chip buffer 27 and transmitted the chips via datastream 25.

FIG. 7 illustrates an example arrangement of the chips within chipbuffer 27. In this arrangement the chips are organized in an arrayhaving M columns and K+L rows. Each row within buffer 27 is filled fromdata stream 21 and stores M chips generated from a common symbol.Chip-interleaving unit 28 read the chips from chip buffer 27 in columnwise format in which each column holds K chips, each chip beinggenerated from a unique one of the K symbols, and L guard chips. Asdiscussed above, block separator 18 stores the received chips in asimilar array. While receiving the interleaved chips from data stream21, however, block separator fills the array column by column, and thenoutputs the data row by row, thereby de-interleaving the chips.

FIG. 8 is a flowchart illustrating an example mode of operation ofcommunication system 2 of FIG. 1 in which transmitter 4 and receiver 6communicate using chip-interleaved block-spread communications.Generally, transmitter 4 parses an outbound serial data stream intoblocks of K symbols (50) and applies a user-specific code of length M toeach of the symbols within the blocks (52). This generates a set of Mchips for each symbol, which transmitter 4 buffers in array format (54)and pads with guard chips (56).

After block-spreading the symbols, transmitter 4 extracts the chips fromthe buffer so as to interleave the chips for the K symbols (58). Thechips that are generated from the same symbol, therefore, are temporallyspaced and separated by the guard chips. In this manner, each block of Ksymbols produces M*(K+L) interleaved chips, where L represents thenumber of guard chips and M represents the maximum number of users thatcan be supported simultaneously. The transmitter converts theinterleaved chips into a serial bit stream (60) and outputs atransmission waveform for carrying the chip-interleaved, block-spreaddata through the communication channel 8 to receiver 4 (62).

Receiver 6 receives the incoming data stream (64) and stores theinterleaved chips in array form (66). Once all of the chips for a blockof symbols have been received and stored, the receiver reads K+L subsetsof the stored chips, each subset having M chips that were generated fromthe same symbol, thereby de-interleaving the chips (68). Receiver 4 thenapplies a matched filter (70) to each subset in order to separate thesymbols for the multiple users based on orthogonality, and then appliesa single-user decoding scheme (72) to remove channel effects and outputthe estimated symbols. Receiver 4 then converts the symbols into serialdata (74).

FIG. 9 is a graph illustrating how the described chip-interleavedblock-spreading (CIBS) technique described herein can increase bandwidthefficiency as the number of symbols K within a block is increased. Inparticular, FIG. 9 illustrates how the maximum number of supported usersM increases as K increases from 2 to 16 symbols per block, where thesystem spreading gain is set to 33. The shift orthogonal CDMA method 80is illustrated for comparison purposes. As a baseline, the conventionalCDMA method used in practice would only allow the number of users to beup to about 25% of the system's spreading gain, which is approximately 8users here; thus, conventional CDMA would allow even less users than theshift-orthogonal CDMA shown in FIG. 9. Plot 82 illustrates modeledresults when the chip-interleaved block-spreading technique is appliedto a communication channel having a length (L+1) of two chips indiscrete time. Plot 84 illustrates modeled results for a communicationchannel when the channel length equals four chips. As can be seen fromFIG. 9, the number of supported users approximately doubles the numbersupported by shift-orthogonal CDMA as the block size is increased from 2to 16 blocks.

FIGS. 10 and 11 are graphs illustrating bit error rate of the CIBStechnique compared to conventional multi-user detection schemes, whichare often much more complex and expensive to implement. FIG. 10illustrates the CIBS technique compared with Direct Sequence (DS) CDMA.FIG. 11 illustrates the CIBS technique compared with Multicarrier (MC)CDMA.

Various embodiments of the invention have been described. The inventionprovides efficient techniques for maintaining the orthogonality of userwaveforms in multi-user wireless communication systems, such as systemsusing code division multiple access (CDMA). Unlike conventional systemsin which spreading is performed on a per symbol basis, thechip-interleaved block-spreading techniques described herein spreadblocks of symbols and interleave the resulting chips. The inventivetechniques can be embodied in a variety of receivers and transmittersincluding base stations, cell phones, laptop computers, handheldcomputing devices, personal digital assistants (PDA's), and the like.The devices may include a digital signal processor (DSP), fieldprogrammable gate array (FPGA), application specific integrated circuit(ASIC) or similar hardware or software. These and other embodiments arewithin the scope of the following claims.

1. A method comprising: applying a user-specific orthogonal spreadingcode to a block of K information bearing symbols to form a set of Mchips for each symbol; storing the chips in an array having M columnsand K+L rows, where L is a function of a channel length of a wirelesscommunication channel; selectively interleaving the chips from the chipsets; and generating a transmission signal from the interleaved chips.2. The method of claim 1, wherein the wireless communication comprises afrequency selective communication channel, and wherein applying thespreading code comprises an orthogonal spreading code selected such thatthe interleaved chips retain their orthogonality after passing throughthe frequency selective communication channel.
 3. The method of claim 1,further comprising communicating the transmission signal through thewireless communication medium.
 4. The method of claim 1, whereingenerating the transmission signal further comprises: padding eachcolumn of the array with L guard chips; and generating the transmissionsignal by reading the chips from the array in column wise fashion. 5.The method of claim 4, wherein the guard chips comprise null values. 6.The method of claim 4, wherein the guard chips are selected from acommon modulation constellation.
 7. The method of claim 1 furthercomprising: receiving the signal; and de-interleaving the chips from thereceived signal.
 8. The method of claim 7 further comprising separatingthe data according to a user.
 9. The method of claim 8, whereinseparating the data comprises applying a matched filter and asingle-user decoding technique.
 10. The method of claim 7, whereinde-interleaving the data comprises storing the chips in an array havingM columns and K+L rows, wherein M represents a number of spreading codeswithin a set of spreading codes, and father wherein the M chips withineach row of the array correspond to a common symbol.
 11. The method ofclaim 10, wherein de-interleaving the data further comprises producing astream of chips by reading the array in row wise fashion.
 12. The methodof claim 11, further comprising: applying a matched filter to the streamof chips to separate signals from different users based on their codeorthogonality and produce a stream of user-specific symbols; applying asingle-user detecting scheme to remove channel effects and outputuser-specific symbol estimates; and converting the stream ofuser-specific symbol estimates into a serial data stream.
 13. Acomputer-readable medium having instructions thereon to cause aprogrammable processor to: apply a user-specific orthogonal spreadingcode of length M to a block of K information-bearing symbols to form aset of M chips for each symbol; and store the chips in an array having Mcolumns and K+L rows, where L is a function of the communication channellength; select chips from the chip sets to produce a stream of chips inwhich the chips from different sets are interleaved; and generate atransmission signal from the stream of interleaved chips.
 14. Thecomputer-readable medium of claim 13, further including instructions tocause the processor to transmitting the signal through a wirelesscommunication channel.
 15. The computer-readable medium of claim 13,further including instructions to cause the processor to: pad eachcolumn of the array with L guard chips; and generate the transmissionsignal by reading the chips from the array in column wise fashion.
 16. Acomputer-readable medium having instructions to cause a processor to:receive a signal having interleaved chips generated from a block of Kinformation-bearing symbols; write the interleaved chips column-wiseinto an may such that each row contains chips generated from the samereceived symbol, wherein the array has M columns and K+L rows, wherein Lis a function of the communication channel length and M represents anumber of spreading codes within a set of spreading codes applied togenerate the signal; and produce a stream of de-interleaved chips byreading the rows of the array.
 17. The computer-readable medium of claim16, wherein the M chips within each row of the array are generated froma common received symbol.
 18. The computer-readable medium of claim 16,wherein the instructions cause the processor to: apply a matched filterto the stream of de-interleaved chips to produce a stream ofuser-specific symbols; apply a single-user channel equalization andsymbol detection scheme to remove channel effects and outputuser-specific symbol estimates; and convert the stream of user-specificsymbol estimates into a serial data stream.
 19. A transmitting devicecomprising: a block-spreading unit to form a set of M chips for eachsymbol of a block of K information-bearing symbols and to produce astream of chips in which the chips from different sets of chips areinterleaved and separated by L guard chips, wherein L is a function of achannel length of a wireless communication; and a pulse shaping unit togenerate a transmission signal from the stream of interleaved chips. 20.The transmitting device of claim 19, wherein the block-spreading unitcomprises: a symbol-spreading unit to generate M user-specificorthogonal spreading chips for each symbol within the block of Ksymbols; a buffer to store the sets of chips; and a chip-interleavingunit to read chips from the buffer and output a stream of chips in whichthe chips from different sets are interleaved.
 21. The transmittingdevice of claim 20, wherein the buffer stores the chips in an arrayhaving M columns and K+L rows, where M represents a maximum number ofusers.
 22. The transmitting device of claim 19, wherein the buffer padseach column of the array with L guard chips.
 23. The transmitting deviceof claim 19, wherein the chip-interleaving unit reads the chips from thearray in column wise fashion.
 24. The transmitting device of claim 20,wherein the transmitting device comprises a cellular phone.
 25. A systemcomprising: a transmitter to transmit a signal through a wirelesscommunication channel according to interleaved chips generated from ablock of K information-bearing symbols, wherein the transmitterinterleaves the chips in an array having M columns and K+L rows, where Lis a function of a channel length of the wireless communication channeland M represents a maximum number of users; and a receiver to receivethe signal and de-interleave the chips.
 26. The system of claim 25,wherein the transmitting device comprises a block-spreading unit to forma set of chips for each symbol of the block and to produce a stream ofchips in which the chips from different sets are interleaved; and apulse shaping unit to generate the signal from the stream of interleavedchips.
 27. The system of claim 26, wherein the block-spreading unitcomprises: a symbol-spreading unit to generate user-specific orthogonalspreading chips codes for each symbol within the block of symbols; abuffer to store the sets of chips in the array form; and achip-interleaving unit to read chips from the buffer and output a streamof chips in which the chips from different sets are interleaved.
 28. Thesystem of claim 25, wherein the receiver comprises: a block separator tostore the interleaved chips column-wise into an array such that each rowcontains chips generated from the same received symbol with intersymbolinterference, and to produce a stream of de-interleaved chips by readingthe rows of the array; a single-user detector to apply a matched filterto the stream of de-interleaved chips to produce a stream ofuser-specific symbols; and a single-user channel equalization and symboldetection scheme to remove channel effects and output the estimatedsymbols.
 29. The system of claim 28, wherein the single-user detectorachieves performance equivalent to a set of M single user detectors. 30.A system comprising: a transmitter to transmit a signal according tointerleaved chips generated from a block of symbols; and a receiver toreceive the signal and de-interleave the chips, wherein the receivercomprises: a block separator to store the interleaved chips column-wiseinto an array such that each row contains chips generated from the samereceived symbol with intersymbol interference, and to produce a streamof de-interleaved chips by reading the rows of the array wherein thearray has M columns and K+L rows wherein L is a function of thecommunication channel length and M represents a number of spreadingcodes with a set of spreading codes applied to generate the signal; asingle-user detector to apply a matched filter to the stream ofde-interleaved chips to produce a stream of user-specific symbols; and asingle-user channel equalization and symbol detection scheme to removechannel effects and output the estimated symbols, wherein thesingle-user detector that achieves performance equivalent to a set of Msingle user detectors.